Method for confirming registration of tracked bones

ABSTRACT

A process for confirming registration of bones involved in a joint replacement procedure is provided that includes a three dimensional (3-D) models of the bones being generated. The bones are tracked with a tracking device attached to each of the bones to allow 6-degrees of freedom (DOF) tracking during the joint replacement procedure. The 3-D models to the bones are registered and the bones having the tracking device are moved. A corresponding motion in the 3-D models with the moving of the bones is then observed. The registration of the 3-D models to the bone when the observations of the 3-D models move in correspondence with the actual bones is then confirmed or an alarm when an algorithm detects the 3-D bone models move unexpectedly during the movement of the bones. A system for confirming registration of bones involved in the joint replacement procedure is also provided.

FIELD OF THE INVENTION

The present invention generally relates to the field of computerassisted orthopaedic surgery and in particular, to a new and usefulprocess and system for confirming registration of tracked bones insurgery.

BACKGROUND OF THE INVENTION

Total joint replacement (TJR) (also called primary total jointarthroplasty) is a surgical procedure in which the articulating surfacesof a joint are replaced with prosthetic components, or implants. TJR,especially for hips, knees, shoulders, and ankles restores functionalitywhile greatly reducing pain associated with osteoarthritis in patients.The benefits of TJR are tempered by complications associated withreplacement misfit. Less than perfect fit of a replacement joint placesunbalanced forces on the implant that can lead to premature implant wearand discomfort. When such wear becomes extreme, revision surgery isrequired.

TJR typically involves the removal of the articulating cartilage surfaceof the joint including a varying amount of bone depending on the jointand the replacement implant being used. This cartilage and bone is thenreplaced with a synthetic, typically metal and/or plastic, implant thatis used to create a new joint surface. The position, orientation andcompliance of the prosthetics implanted into the joint are criticalfactors that have a significant effect on the clinical outcome of thepatient. Therefore, computer assisted surgical devices are gainingpopularity as a tool to pre-operatively plan and precisely execute theplan to ensure an accurate final position and orientation of theprosthetics within the patient's bone that can improve long termclinical outcomes and increase the survival rate of the prosthesis. Ingeneral, the computer assisted surgical systems include two components,an interactive pre-operative planning software program and a computerassisted surgical device that utilizes the pre-operative data from thesoftware to assist the surgeon in precisely executing the procedure.

The conventional interactive pre-operative planning software generates athree dimensional (3-D) model of the patient's bony anatomy from acomputed tomography (CT) or magnetic resonance imaging (MRI) imagedataset of the patient. A set of 3-D computer aided design (CAD) modelsof the manufacturer's prosthesis are pre-loaded in the software thatallows the user to place the components of a desired prosthesis to the3-D model of the boney anatomy to designate the best fit, position andorientation of the implant to the bone. The user can then save thispre-operative planning data to an electronic medium that is loaded andread by a surgical device to assist the surgeon intra-operatively inexecuting the plan.

Additionally, one of the main goals of computer-assisted surgery is todefine a patient specific plan and precisely execute the procedure, in atimely manner on a patient. The accuracy of the cut volume for a givenimplant is critical and errors can accumulate based on registrationerror, cutter manufacturing tolerances and implant manufacturingtolerances. Registration techniques well known in the art such as pointto surface registration can align the coordinate frames of a patient'sbone to the coordinate frames of a 3-D model of a patient's bone and tothe coordinate frame of the surgical device.

The registration of the location of the bone intra-operatively withinthe workspace of a surgical robot serves to determine the preciselocation and orientation of the bone within the workspace of the robot.In some embodiments, this may be accomplished by probing radiopaquefiducial markers placed into or on the bone that were installed prior topre-operative imaging. A fiducial marker is appreciated to be a materialwith an opacity that is different than that of surrounding subjecttissue or a reference point capable of detection by an external source(e.g. optical cameras, x-rays, radio frequency). Examples of fiducialmarkers include a radiopaque pin, an active device such as radiofrequency identification (RFID) tag or light emitting diode (LED), apassive retro-reflective sphere, or a combination thereof. In stillother inventive embodiments, a registration guide is applied that fitson the bone, or a surface matching algorithm is used, or any othermethod to determine the orientation of the subject's operative bone. Theusage of such techniques are further detailed in: PCT/IB2013/002311entitled SYSTEM AND METHOD FOR REGISTRATION IN ORTHOPAEDIC APPLICATIONS.S. Cohan, “ROBODOC achieves pinless registration” The Industrial Robot;2001; 28, 5; pg. 381. P. J. Besl, “A Method for Registration of 3-DShapes” IEEE Transactions on Pattern Analysis and Machine intelligence,1992; 14, pgs. 239-256.

Once the registration is complete, it is imperative that theregistration is verified and remains accurate throughout the entireprocedure. If a tracking system monitors the POSE of the registered bonevia tracking arrays fixed thereto, any relative movement between thetracking array and the bone negates the accuracy of the registration. Ifthe bone is not re-registered, the procedure cannot be executedaccording to the plan. Often, the tracking array is bumpedunintentionally and there is no method for signaling or alerting thesurgeon that the registration is no longer accurate. Or, the fixedtracking array may drift over-time accumulating errors in theregistration. It is not until the surgeon notices the computer-assisteddevice is off-target or there is an erroneous reading on the device tosuggest the registration is compromised.

Additionally, there is no intuitive visual process for verifying theaccuracy of the registration. In certain registration procedures, afinal verification step may be implemented which involves digitizingseveral additional points on the bone after the registration iscomplete. The additional points confirm and verify the POSE of the bone.A prompt may then indicate that the registration was successful.However, this verification process can increase the surgical time.

Finally, after the TJR is complete, the surgeon may articulate the jointto ensure the proper range of motion and kinematics are achieved. It maybe desirable to restore the joint to a similar joint motion, kinematics,or articulation as the pre-cut anatomy so the soft tissues are wellbalanced, and there is decreased stress on the surrounding muscles andother anatomical structures. Having a process to compare thearticulation of the now modified joints to the pre-articulating motionmay be highly beneficial for assessing not only the outcome of theprocedure, but to also provide a mechanism for recommendingintraoperative modifications for the joint to achieve thepre-articulating motion.

Thus, there exists a need for a system and process to verify and monitorthe accuracy of bone registration prior to and during acomputer-assisted surgical procedure. There further exists a need for aprocess to articulate a joint prior to making any cuts, so as to comparethe articulation after the trial implants are in place to see thedifferences, and possibly recommend corrections so as to obtain asimilar articulation as the pre-cut anatomy. There further exists a needto rely on this comparison as a way to recommend adjustments to thetibial internal-external rotation in knee replacement TJR.

SUMMARY OF THE INVENTION

A process for confirming registration of bones involved in a jointreplacement procedure is provided that includes a three dimensional(3-D) models of the bones being generated. The bones are tracked with atracking device attached to each of the bones to allow 6-degrees offreedom (DOF) tracking during the joint replacement procedure. The 3-Dmodels to the bones are registered and the bones having the trackingdevice are moved. A corresponding motion in the 3-D models with themoving of the bones is then observed. The registration of the 3-D modelsto the bone when the observations of the 3-D models move incorrespondence with the actual bones is then confirmed or an alarm whenan algorithm detects the 3-D bone models move unexpectedly during themovement of the bones.

A system for confirming registration of bones involved in a jointreplacement procedure includes a high definition (HD) camera mounted ona surgical light. An integrated tracking system for tracking theposition and orientation of each of the bones is provided. One or moremarker light emitting diodes (LEDs) are fitted on each of the bonesprior to registration. A display is adapted to show a three-dimensional(3-D) reconstructed picture of the bones from a perspective of said HDcamera or an outline of a model of the bones superimposed on video fromsaid HD camera.

A system for confirming registration of bones relative to a trackingsystem by the process includes a tracking array attached to a bone of apatient with one or more marker LEDs mounted to each of the bones. Atracking system is provided to monitor the relative position between thetracking array and the one or more marker LEDs after bone registration.The tracking system generates an alert if there is relative movementbetween the tracking array and one or more marker LEDs mounted on thebone.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is further detailed with respect to the followingdrawings. These figures are not intended to limit the scope of thepresent invention but rather illustrate certain attributes thereof.

FIG. 1 illustrates a 3-D model of the operative bones of a knee jointreplacement procedure;

FIG. 2 illustrates a process flowchart according to the presentinvention;

FIG. 3 illustrates a collision between 3-D models of the operative boneswhile a surgeon moves the actual bone;

FIG. 4 illustrates system for the verification of bone registrationusing a high definition (HD) camera mounted on a surgical light andincluding an integrated tracking system.

FIGS. 5A and 5B, illustrates a tracking array with an LED that highlighta relative position on the operative bone to monitor registrationaccuracy.

FIG. 6 illustrates a single fiducial marker mounted on the bone relativeto a tracking array attached to the bone to monitor registrationaccuracy.

FIG. 7 illustrates a process flowchart for comparing a virtual motion toa physically tracked bone motion according to embodiments of theinvention.

DESCRIPTION OF THE INVENTION

The present invention has utility as a system and process for confirmingthe registration of tracked bones prior to and during acomputer-assisted surgical procedure. Embodiments of the inventiveprocess and system confirm registration of a subject's bones byarticulating the physical tracked bones relative to 3-D displayed modelsof the tracked bones. The articulation of the physically tracked bonesand corresponding motion of the 3-D displayed models may be further usedto adjust the bone orientation or provide intraoperative jointmodification recommendations for improved artificial joint positioning,as compared to conventional techniques.

The following description of the preferred embodiments of the inventionis not intended to limit the invention to these preferred embodiments,but rather to enable any person skilled in the art to make and use thisinvention. The invention described herein illustratively uses total kneearthroplasty as an example. Although total knee arthroplasty is oneprocedure that can benefit from the disclosed embodiments other surgicalprocedures can illustratively include surgery to the hip joint, spine,shoulder joint, elbow joint, ankle joint, jaw, a tumor site, joints ofthe hand or foot, and other appropriate surgical sites.

As used herein, a fiducial marker refers to a point of reference capableof detection. Examples of a fiducial marker may include: an activetransmitter, such as a light emitting diode (LED) or electromagneticemitter; a passive reflector, such as a plastic sphere with aretro-reflective film; a distinct pattern or sequence of shapes, linesor other characters; acoustic emitters or reflectors; magnetic emittersor reflectors; radiopaque markers; and the like or any combinationsthereof. A tracking array is an arrangement of a plurality of fiducialmarkers in/on a rigid body of any geometric shape, where each trackingarray has a unique geometry of fiducial markers or a unique blinkingfrequency if active LEDs are used to distinguish between each of thetracked objects.

Disclosed herein is the use of a tracking system. Optical trackingsystems generally include at least two receivers to detect one or morefiducial markers in three-dimensional space. The receivers are incommunication with at least one processor for processing the receiveroutput. The processing determines the position and orientation (pose) ofa tracking array using various algorithms such as time-of-flight ortriangulation. The receiver may detect the location of a fiducial markerthrough a variety of mechanisms including, but not limited to, visiblelight, electromagnetic radiation, and infrared, as well as any shape,pattern, line, sequence or character recognition. It should beappreciated that other tracking systems known in the art may be used totrack objects using radio frequency, magnetics, accelerometers,gyroscopes, acoustic energy or signals, and mechanical linkages.Examples of tracking systems to determine the pose of an object aredescribed in U.S. Pat. Nos. 5,282,770, 6,061,644, and 7,302,288. Anexample of a mechanical tracking system having mechanical linkages isdescribed in U.S. Pat. No. 6,322,567.

Also referenced herein are computer-assisted devices which are to beconsidered synonymous with computer-aided surgical system, roboticsurgical systems, navigation assisted surgical system, image-guidedsurgical systems and the like. The computer-assisted device may be, forexample, a 2-6 degree of freedom hand-held surgical system, a serialchain manipulator system, a parallel robotic system, or a master-slaverobotic system, as described in U.S. Pat. Nos. 5,086,401, 7,206,626,8,876,830, and 8,961,536, U.S. Pat. App. No. 2013/0060278 and U.S. Prov.App. 62/054,009. Such commercial systems illustratively include forexample the NavioPFS™ Robotic Resurfacing System (Blue BeltTechnologies), the RIO® Robotic System (Mako Surgical Corp.), and theTSolution One™ Surgical System (Think Surgical). It should beappreciated that navigated or tracked instruments may also be used withthe subject matter disclosed herein.

A process is provided to confirm the registration of bones involved in ajoint replacement procedure. The process includes the use ofpre-operative planning software to generate a 3-D model of the patient'sbony anatomy from a computed tomography (CT) or magnetic resonanceimaging (MRI) image dataset of the patient. A set of 3-D computer aideddesign (CAD) models of the manufacturer's prosthesis are pre-loaded inthe software that allows the user to place the components of a desiredprosthesis to the 3-D model of the boney anatomy to designate the bestfit, position and orientation of the implant to the bone. This isaccomplished with commercially available systems such as the RIO®Interactive Orthopedic System manufactured by Stryker Mako (Ft.Lauderdale, Fla.) and the TSolution One™ Surgical System manufactured byTHINK Surgical, Inc. (Fremont, Calif.). An exemplary 3-D modeling of ajoint that will be subject to replacement is illustrated in FIG. 1. FIG.1 depicts a 3-D model of a knee joint including a coronal and sagittalview of the distal femur 12 and proximal tibia 14. The 3-D virtualmodels may be displayed on a monitor 10 to facilitate pre-operativeplanning or to monitor the motion of the tracked bonesintra-operatively.

A computer simulation may be run to optimize the multiple variables ofpositional and rotational degrees of freedom to achieve an optimizedartificial joint geometry. A finite element analysis is readily appliedbased on these variables to achieve a balanced force weighting onopposing sides of the joint through a preselected swing angle for thejoint. It is appreciated that patient weight, height, and arm swingcounterbalance are additional factors that can be built into theoptimization routine to predict optimal joint arthroplasty positioning.An example of analyzing the positional and geometric rotational degreesof freedom using a computer simulated model is described in A. C. Godestet al., “Simulation of a knee joint replacement during a gait cycleusing explicit finite element analysis” Journal of Biomechanics 35(2002) 267-275.

With reference to FIG. 2, an inventive process schematic is showngenerally at 20. The three dimensional (3D) models of operative bonesinvolved in a joint replacement procedure are generated, as a physicalor virtual model at step 22 and is made available to the surgeon duringthe procedure. The virtual models may be part of an overall surgicalplan that further includes instructions for a computer-assisted surgicaldevice, the final implant position, or the results of any such computersimulations generated for the optimal position of the bones or implantsat step 24.

A tracking device such as a tracking array or a mechanical trackingprobe is attached to each operative bone to allow 6-degrees of freedom(DOF) tracking during the procedure at 26. The bones may be tracked by atracking system as previously described. The 3D models of each operativebone are then registered to the patient's actual operative bone at step28. Systems and methods of optical or mechanical tracking andregistration are described in U.S. Pat. No. 6,033,415, which isincorporated herein by reference in its entirety. Systems and processesfor pre-operative planning and precise bone removal are also known tothe art and include those detailed in WO 2015006721 A1.

At step 30, the surgeon moves a tracked bone having a tracking deviceassociated therewith, and a display shows a virtual representation ofthe motion in real-time. As a result, a surgeon can observe the positionof the bones involved in the joint arthroplasty in a way that isimpossible from viewing the actual bones. This attribute of the presentinvention is a novel attribute that becomes increasingly helpful as thebones tagged with a tracking device approach the optimal positioning. Insome inventive embodiments, the display or jig include feedbackindicators such as markers, a blinking screen, arrows, or highlightedareas on the virtual bone models, that may be used to indicate or guidethe surgeon to an optimal position and orientation of a given bone basedon the pre-surgical plan and any simulations associated therewith. Thesurgeon may then assess the kinematics of the operative bones in theposition and orientation defined by the pre-surgical plan prior tomaking any bone cuts.

In a particular embodiment, the surgeon or system determines if themovements of the tracked bones correspond to the movements of the 3-Dmodels at step 32. If the tracked bones are moving in correspondencewith the 3-D models then the surgeon can confirm that the registrationis accurate at step 34. If the tracked bones do not move incorrespondence with the 3-D models, or the motion is unexpected, thenthe accuracy of the registration is likely not accurate. In that case,the surgeon re-registers the bone. This is described in more detailbelow.

In an illustrative example of a specific applications of the invention,with respect to FIG. 3, the surgeon may verify or confirm the accuracyof the registration by making sure that the tracked femur and tibia donot collide by viewing the 3-D models on a display 40 (e.g. monitor,television); or that the femoral head stays approximately in the centerof the acetabulum during articulation of the femur relative to thepelvis, each tracked, by viewing the 3-D models on the display 40 duringarticulation. This provides an intuitive visual process for confirmingthe accuracy of the bone registration. If, for example, the 3D virtualmodel of the femur 42 appears to impinge or collide with the 3D virtualmodel of the tibia 44 throughout articulation as seen in the boundingcircle 46, or the femoral head rotates outside the center of theacetabulum, then the registration is likely not accurate and the surgeoncan re-register the bone before proceeding with the procedure. If theregistration appears accurate, the surgeon may confirm or verify theregistration by way of an input mechanism (e.g. mouse, keyboard,joystick, pendant, touchscreen display, microphone) in communicationwith the tracking system or computer-assisted device. A prompt 48 may bedisplayed on the display 40 for the surgeon to select whether theregistration is confirmed or not. The surgeon may also confirm theregistration to the system or device by providing a particular signal tothe tracking system. For example, the surgeon can place a trackeddigitizer probe in a specific location relative to the 3-D bone model,or manipulate the bones in a particular pattern or shape. Therefore, thesurgeon to quickly confirm the registration without having to use aninput mechanism.

It should be appreciated that the surgeon can monitor and confirm theregistration throughout an entire procedure by moving the tracked bonesand visualizing the corresponding motion of the 3-D virtual models onthe display. In certain applications, such as TKA, articulating thejoints throughout flexion/extension are normal steps of the procedure.Therefore, confirming the registration throughout these normalprocedural steps is quick, efficient, and does not require anyadditional steps outside of a normal TKA. Additionally, by viewing suchmodels devoid of skin, connective tissue, fat, and blood providesinsights not available to a surgeon through actual inspection of thejoint before or during surgery.

In an inventive embodiment, collision detection may be implemented witha computer program or through other types of algorithms that provide awarning to a surgeon or other medical personnel if the 3D virtual modelscollide during the articulation of the tracked bones. One example of acollision detection algorithm that can be modified by one of skill inthe art to warn a surgeon of inaccurate registration is described inMadera-Ramírez, Francisco. “An Introduction to the Collision DetectionAlgorithms.” Abstraction and Application Magazine 5 (2014). Otheralgorithms can also be implemented to provide a warning or alert thesurgeon that the corresponding motion of the 3-D virtual models isoutside of specified thresholds. For example, the algorithm may monitorthe relative rotation of the femur with respect to the center of theacetabulum. If the femoral head does not rotate within ±2 mm of thenatural center of the acetabulum, then an alert may be generated. Inanother example, an alert be generated if the bone models move apartbeyond a threshold limit. In TKA, if the closest point between the tibiaand either the medial or lateral condyle region of the distal femurbecomes significantly greater than the expected total cartilagethickness or other specified distance threshold, the registration islikely off or the tracking arrays may have moved relative to the bone,and an alert is generated.

In certain inventive embodiments, registration of tracked bones may alsobe confirmed by observing the full extension position of a subject'slimb and compare the limb extension to the virtual full extensionposition to make sure that the achieved extension is correct.Furthermore, as a comparison control, a measurement of the articulationof the joint prior to making any surgical or altering cuts may be savedfor later comparison with a post treatment or operative articulation fora measurement of alignment after the trial implants are in place to seethe differences, and possibly recommend corrections. As a result, asurgeon can obtain joint positions that retain pre-cut bone positions orcontrolled modification of dysfunctional pre-cut geometries. In aspecific inventive embodiment, a pre- and post-operative comparison maybe used as a way to recommend adjustments for the subject's tibiainternal-external rotation.

Furthermore, surgical errors during bone resection may lead to abnormaljoint motion after trial implantation, and specific embodiments of theinvention are used to visualize the abnormal joint motion, where theoperative bones, with trial implants, are tracked during motion, and 3-Dmodels of the pre-operative bones are displayed rather than thepost-operative bones. Any abnormal motion, such as collisions betweenthe bones, would indicate changes in joint kinematics and may be used todirect the surgeon's choice of intraoperative correction For example, inTKA, if a collision detection algorithm detects ±2 mm of collision invarus-valgus rotation between the medial femoral condyle and the medialaspect of the tibia, the computer-assisted device or tracking system mayrecommend to the surgeon via a prompt on a display, that 2 mm of themedial aspect of the tibia should be resected to obtain the pre-cutarticulating motion of the knee. These recommendations can be extendedto other alignment characteristics such as the tibial slope,internal-external rotation of the femoral or tibial component,varus-valgus rotation, mechanical axis alignment, kinematic alignment,ligament balancing, soft tissue balancing, flexion/extension gap, andany combinations thereof to achieve the pre-cut anatomical articulation.

FIG. 7 generally outlines another process 90 using the physicalarticulation of the tracked bones to provide bone modificationrecommendations and/or further aid a surgeon in obtaining apre-operatively planned result. The generation of the 3-D bone models(step 92), and the planning of the placement of the virtual implantsrelative to the bone models (step 94) with or without the aid of thecomputer simulations (step 96), are all accomplished as described above.Next, the virtual motion of the 3-D bone models with the virtualimplants is simulated. The surgeon may further adjust the plannedposition of the virtual implants to achieve a desired virtual motionthat the surgeon prefers the actual bone motion to mimicpost-operatively. The desired virtual motion is then saved at step 98for use intra-operatively. At step 100, the surgeon executes theprocedure and modifies the bone according to the plan as describedabove. After modifying the bone, trial components are placed in thejoint and the surgeon physically articulates the tracked bones at step102. The saved virtual motion is then compared with the actualarticulation of the tracked bones at step 104. In a specific embodiment,the saved virtual motion of the 3-D bone models with the virtualimplants are overlaid on the 3-D bone models registered to the actualbones. To ensure the saved virtual motion corresponds with the physicalmotion, one of the virtual bones or a portion of one of the virtualbones is mapped to one of or a portion of the 3-D bone model registeredto the actual bone. For example, the femoral head and neck of thepre-operative virtual model associated with saved virtual motion ismapped to the femoral head and neck of the virtual model registered tothe bone. Therefore, the surgeon can observe how the actual motion ofthe non-mapped bone corresponds to the saved virtual motion of thenon-mapped bone. For TKA, the mapped bone may be the femur, where thesurgeon can observe how the actual tibia moves in relation to the actualfemur and compare this to how the virtual tibia moved relative to thevirtual femur during planning. The surgeon may have the ability tospeed-up and slow-down the virtual motion, or stop the virtual motion atparticular articulation points, to aid in the comparison. If the motionsare similar, the surgeon can complete the procedure (step 106) byinserting the final implants and closing the surgical site. If themotions are dissimilar, the computer-assisted system may providerecommendations (step 108) to re-modify the bone such that the actualbone motion corresponds with the saved virtual motion.

In FIG. 4, a particular embodiment of a system is shown generally at 50for facilitating embodiments of the aforementioned processes includingthe confirmation, verification and monitoring of bone registration. Thesystem 50 may include a high definition (HD) camera 52 mounted on asurgical light 54 that has an integrated tracking system with opticalreceivers 56. The HD camera 52 may be calibrated to a tracking systemusing one or more marker light emitting diodes (LEDs) 58 fitted on thebone B prior to registration, and then during a post-registrationassessment, a 3D reconstructed picture of the bone model from the HDcamera's perspective, or an outline of the bone model 60 from thatperspective, could be superimposed on the video 62 from the camera 52,and this should visually correspond to the image of the bone B in thevideo 62. If, for example, the tracking array 64 on the bone B shouldmove, or be bent during the procedure, the superimposed bone model 60would shift away from being aligned with the bone B in the video 62.This would give the surgeon an easily checked indication in real-time ofwhether the registration is still fundamentally accurate.

In a specific inventive embodiment, with respect to FIGS. 5A and 5B, anLED 74 on the tracking array 70 is used to illuminate a particularlandmark or manually made mark 76 on the bone B. The tracking array 70shown here includes passive fiducial markers 72 and an LED 74 capable ofhighlighting an arbitrary spot on the bone B. For example, once thetracking array 70 is attached to the bone B, this LED 74 illuminates asmall spot in an arbitrary location on the bone B, the surgeon wouldthen mark that spot 76 with a marking device, illustratively including apurple pen, and then proceed to do the registration. If the trackingarray 70 moves relative to the bone B during registration or theprocedure, the highlighted spot will almost certainly move away from themarked purple spot 76, indicating a registration error. In a specificinventive embodiment, a distance measurement device, illustrativelyincluding a laser or possibly an LED mechanism 74 may be attached to thetracking array 70. The distance measurement device may be pointed at thebone and would detect a change in distance if the tracking array movedrelative to the bone.

In an inventive embodiment, with respect to FIG. 6, a single fiducialmarker 82 is mounted on the bone B, in relation to a tracking array 80attached to the bone to provide a redundant reference for monitoring anyrelative motion between the fiducial marker 82 and the tracking array80. After registration, if the tracking array 80 were to move or bend,the tracking system would see the geometry change between the trackingarray markers 84 and the single fiducial maker 82. An alarm or promptmay be triggered to alert the surgeon that the tracking array 80 hasmoved relative to the bone indicating the registration is no longeraccurate. In an embodiment, the fiducial marker 82 may be a single LEDpowered with a small embedded battery, which would most likely be adisposable battery.

In specific inventive embodiments, two full markers are attached to abone at a given location, with a main marker and a smaller, lessaccurate marker, to check that the relative transform between themarkers remains stable. Furthermore, a digitizer may be used as neededto recheck a particular landmark or manufactured mark, such as a purplepen mark, if any question on the registration arises.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of thedescribed embodiments in any way. Rather, the foregoing detaileddescription will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments.It should be understood that various changes can be made in the functionand arrangement of elements without departing from the scope as setforth in the appended claims and the legal equivalents thereof.

The foregoing description is illustrative of particular embodiments ofthe invention, but is not meant to be a limitation upon the practicethereof. The following claims, including all equivalents thereof, areintended to define the scope of the invention.

1. A process for confirming registration of bones involved in a jointreplacement procedure, said process comprising: generating a threedimensional (3-D) models of the bones; tracking the bones with atracking device attached to each of the bones to allow 6-degrees offreedom (DOF) tracking during the joint replacement procedure;registering the 3-D models to the bones; moving the bones having thetracking device; observing a corresponding motion in the 3-D models withsaid moving of the bones; and confirming the registration of the 3-Dmodels to the bone when the observations of the 3-D models move incorrespondence with the actual bones or providing an alarm when analgorithm detects the 3-D bone models move unexpectedly during themovement of the bones.
 2. The process of claim 1 wherein the 3-D modelsare virtual and said observing is on a video display.
 3. The process ofclaim 1 wherein the registration is confirmed to a computer-assistedsurgical system using an input mechanism in communication with thecomputer-assisted surgical system.
 4. The process of claim 1 furthercomprising re-registering the 3-D models to the bone if the observationsof the 3-D bone models collide.
 5. The process of claim 1 furthercomprising re-registering the 3-D models to the bone if the observationsof the 3-D models rotate outside of a known anatomical region.
 6. Theprocess of claim 5 wherein the bones are a femur and an acetabulum andthe 3-D models are re-registered to the bones when the observations ofthe femur 3-D model rotates outside the center of the acetabulum 3-Dmodel.
 7. The process of claim 1 further comprising re-registering the3-D models to the bone if the observations of a first 3-D bone model isseparated from a second 3-D bone model beyond a specified thresholddistance.
 8. The process of claim 7 wherein the specified thresholddistance is an expected cartilage thickness on the end of one or morebones.
 9. The process of claim 1 further comprising simulating operationof the bones as a joint to yield an optimal configuration and displayingthe optimal configuration on the corresponding motion in the 3-D models.10. The process of claim 1 wherein the said alarm is present providingan alarm when an algorithm detects the 3-D bone models move unexpectedlyduring the movement of the bones.
 11. The process of claim 10 whereinthe unexpected movements of the 3-D bone models is a movement beyond aspecified threshold distance between the 3-D bone models.
 12. Theprocess of claim 11 wherein the specified threshold distance is adistance greater than an expected cartilage thickness.
 13. The processof claim 10 wherein the bones is a femoral head and an acetabulum andthe unexpected movements of the 3-D bone models is a rotation of thefemoral head 3-D model outside of the center of the acetabulum 3-Dmodel.
 14. A system for confirming registration of bones involved in ajoint replacement procedure of claim 1, said system comprising: a highdefinition (HD) camera; said HD camera mounted on a surgical light; anintegrated tracking system for tracking the position and orientation ofeach of the bones; one or more marker light emitting diodes (LEDs)fitted on each of the bones prior to registration; and a display adaptedto show a three-dimensional (3-D) reconstructed picture of the bonesfrom a perspective of said HD camera or an outline of a model of thebones superimposed on video from said HD camera.
 15. A system forconfirming registration of bones relative to a tracking system by aprocess of claim 1, said system comprising: a tracking array attached toa bone of a patient; one or more marker LEDs mounted to each of thebones; a tracking system to monitor the relative position between thetracking array and the one or more marker LEDs after bone registration;and wherein said tracking system generates an alert if there is relativemovement between the tracking array and one or more marker LEDs mountedon the bone.